The present invention relates to disc brakes for vehicles, and in particular to a system for retaining brake pads in disc brakes, such as air-operated disc brakes utilized on commercial vehicles.
Pneumatically-operated disc brakes have been undergoing development and deployment on commercial vehicles since at least the 1970's, and are beginning to replace drum-style brakes due to advantages in areas such as cooling, fade resistance and serviceability. German Patent Publication No. DE 40 32 886 A1, and in particular FIG. 1 of this document, discloses an example of such an air disc brake. In this design, a pneumatic diaphragm chamber (pneumatic actuator) is attached to a rear face of the disc brake caliper housing, and applies a brake actuation force through a linear actuator rod to a brake actuator lever within the caliper. The brake's actuator lever in turn transfers and multiplies the force applied by the actuator rod to one or more spindles, which force brake pads against a brake disc or rotor. The terms “brake disc,” “rotor” and “brake rotor” are used interchangeably herein.
In applications such as commercial vehicles, wheel rims have historically been sized to only provide adequate clearance for the drum-type brakes historically employed on such vehicles. Because the resulting space envelope between the wheel and its axle is limited, the outer radius of the brake caliper, brake pads and any brake pad retention devices must conform to the limited available radial space. Brake pads typically have been located and retained on one of the brake caliper or brake caliper carrier/mount using transverse suspension pins and/or using leaf spring-type metal strips disposed over the outer radius of the brake pads. Brake pads have also been retained by capturing the brake pads between the caliper mounting frame and the portion of the brake caliper which straddles the brake disk. As one of ordinary skill will recognize, the same brake pad support function may be provided by a brake caliper carrier/mount designed to support the brake pads or by a brake pad carrier which is separate from the caliper mounting structure. For convenience in this description, the terms caliper carrier, caliper mount and brake pad carrier may be interchanged without intending to limit the brake pad supporting structure to any specific brake pad and brake caliper carrying structure.
A problem with the previous brake pad retention approaches is their tendency to allow the brake pad to rotate about an axis parallel to the brake disc rotation axis during brake application. This in-place rotation is referred to as “pad kick,” a motion that can generate undesired brake application noise due to brake pad vibrations, increase fatigue damage to the typical over-pad leaf spring retainer, and increase wear and damage to the brake pad and/or brake caliper mounting structure. An illustration of pad kick is provided in FIG. 10. When a brake pad 101 is applied against a friction surface of a brake disk (not illustrated) which is rotating in direction DR, the brake disk's rotation induces motion and reaction forces between the brake pad 101 and its adjacent mount abutment surfaces (not illustrated). At the leading edge 102 of the brake pad the brake pad attempts to move upward in direction LU in response to the friction forces along the face of the brake pad (illustrated here by force arrows across the face of brake pad 101). At the trailing edge 103 of the brake pad, the brake pad attempts to move downward in direction TD. However, because the brake pad 101 is constrained by adjacent mount abutment surfaces, the overall motion of the brake pad is generally a rotation about an axis parallel to the brake disk rotation axis. This motion may be unilateral during the brake application, or may manifesting itself as a moderate-to-severe oscillation of the brake pad in its mount, significantly increasing wear of the abutting brake pad and mount surfaces.
One approach to addressing these and other problems is disclosed in U.S. patent application Ser. No. 14/939,748, which teaches a brake pad mounting and retention arrangement and method of installation and removal in which one or both of the brake pads is pulled upward (i.e., radially outward) by a spring reaction bar and springs over each brake pad. This approach biases surface features at the lateral sides of the brake pad against the undersides (i.e., radially inner sides) of corresponding surface features of the brake pad carrier structure.
The present invention further minimizes the radial height required to provide the desired radially outward biasing of the brake pad. This is accomplished by incorporating at least one brake biasing feature into the structure of the brake pad carrier (also referred to as a carrier mount or carrier frame) in the carrier's brake pad support abutments adjacent to the lateral sides of the brake pad, for example, in the pad carrier mount horns adjacent to the brake pad. The biasing features apply an upward biasing force to corresponding force-receiving features of the brake pad, such as short projections extending laterally from the sides of the brake pad.
In a preferred embodiment, two biasing features are present in the form of spring-loaded plungers that are inset into corresponding bores in the carrier horns, positioned to apply upward biasing forces to the corresponding brake pad lateral projections. The biasing plungers may take any shape that permits their reliable upward movement, i.e., without twisting sideways in their bores to the point of jamming in the bore. For ease of assembly and low manufacturing cost, preferably the biasing plungers and their corresponding bores are generally cylindrical (although any suitable shape may be used).
The biasing plungers and the brake pads should be sufficiently wide in the direction parallel to the brake disc rotation axis to ensure that at least a portion of the biasing plunger remains under at least a portion of the brake pad lateral projection over the course of the brake pad life, i.e., from new brake pad friction material thickness to the friction material minimum thickness wear limit. This arrangement is desired to ensure that the plungers continue to provide the desired upward biasing force on the brake pad as the pad friction material wears.
In a further embodiment of the invention, the biasing plunger and/or the corresponding bore in which the plunger is received may be provided with a groove configured to receive a sealing element, such as an O-ring. The O-ring would assist in preventing, or at least minimizing, the accumulation of water and/or debris if the receiving bore is formed as a blind hole. Preferably the tolerances of the groove and the sealing element are controlled to exclude debris, while permitting the passage of air to the extent needed to avoid forming a vacuum beneath the biasing plunger that would inhibit the application of upward biasing force to the brake pad.
The biasing arrangements of the present invention may also include laterally-oriented retaining pins arranged to engage the brake pad biasing plungers from the side in order to remove the biasing forces of the plungers from the brake pad down during pad installation and removal
The integrated upward biasing features of the present invention may be incorporated into either or both of the outboard and inboard sides of the brake pad carrier. Incorporating these features into the inboard side (the side on which the brake application portion of the brake caliper is located) is particularly advantageous, significantly reducing the vertical space otherwise required to accommodate a brake pad biasing structure above the brake pad.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.